Whisker reinforced ceramic cutting tool and composition thereof

ABSTRACT

A ceramic composition produced by the consolidation of a blend of starting components. The composition comprises a matrix with one or more of the carbides, nitrides and carbonitrides of hafnium, molybdenum, zirconium, tantalum, niobium, vanadium and tungsten, titanium nitride, and titanium carbonitride in an amount that is greater than 50 volume percent of the matrix. The matrix comprises between 60 and 99.8 volume percent of the composition. Ceramic whiskers are uniformly dispersed throughout the matrix wherein the ceramic whiskers comprises between 0.2 and 40 volume percent of the composition.

BACKGROUND OF THE INVENTION

The present invention pertains to a ceramic cutting tool, and acomposition thereof, that has whisker reinforcement. More specifically,the invention pertains to a ceramic cutting tool, and a compositionthereof, that has ceramic whisker reinforcement wherein at least 50volume percent of the ceramic matrix comprises a carbide, nitride and/orcarbonitride of titanium, hafnium, molybdenum, zirconium, tantalum,niobium, vanadium and/or tungsten.

In the past, there have been ceramic bodies with whisker reinforcementsuch as that disclosed in U.S. Pat. No. 4,543,345 to Wei. The Wei Patentdiscloses an alumina matrix with silicon carbide whisker reinforcement,a boron carbide matrix with silicon carbide whiskers, and a mullitematrix with silicon carbide whiskers. According to the Wei patent, theincorporation of silicon carbide whiskers increased the fracturetoughness of the substrate.

Japanese Publication No. 63-10758 to Yamagawa et al. pertains to aceramic composite that comprises alumina as its main component. Thebalance comprises between 5 to 40 weight TiC and 2 to 40 weight percentsilicon carbide whiskers. The combined amount of titanium carbide andsilicon carbide whiskers cannot exceed 50 weight percent, i.e., it is 50weight percent or less. This document also mentions that there can be upto 10 weight percent of an oxide, carbide or nitride of aluminum,silicon and the Group IVa, Va and VIa elements.

U.S. Pat. No. 4,507,224 to Toibana et al. makes general reference tocertain nitrides and carbides as suitable matrix material, along withelectroconductive powder, for SiC fiber reinforcement. The SiC fibersare present in an amount between 5 and 50 weight percent. The '224patent makes specific reference to matrices of silicon nitride, aluminumnitride, boron nitride, silicon carbide, boron carbide, and titaniumcarbide. The '224 Patent recites examples that use alumina, zirconiumoxide, silicon nitride as matrices along with silicon carbide fibers.The focus of the '224 Patent is on a ceramic article suitable forelectric discharge machining. In this regard, the specification statesthat the electrical resistance of the substrate must not exceed 10ohm-cm The publication “Fiber Reinforced Ceramics: A Review andAssessment of their Potential” by Kpochmal (at pages 9 through 16)mentions ceramics (with fiber reinforcement) having a HfC or ZrC matrix.The filaments include tungsten, molybdenum, tantalum, boron, carbon,silicon carbide, boron carbide, and alumina.

There have also been ceramic cutting tools with whisker reinforcement.In this regard, U.S. Pat. No. 4,789,277 to Rhodes et al. discloses theuse of ceramic whiskers (the content ranges from 2 volume percent to 40volume percent) such as alumina, aluminum nitride, beryllia, boroncarbide, graphite, silicon carbide (preferably), and silicon nitride ina ceramic matrix. The ceramic matrix is preferably alumina, but includesalumina “doped” with up to 30% zirconia, hafnia and titanium carbide.The alumina remains the dominant component of the matrix.

PCT\US 86\00528 Patent Application to Rhodes et al. entitled HIGHDENSITY REINFORCED CERAMIC BODIES AND METHOD OF MAKING SAME has as itsfocus the pressureless sintering of whisker-reinforced ceramic bodies.This document mentions a whisker content of between 0.5 and 21 volumepercent. The specific examples teach the use of an alumina matrix withSiC whisker contents from 6.1 volume percent to 29.2 volume percent.

U.S. Pat. No. 5,059,564 to Mehrotra et al. for an ALUMINA-TITANIUMCARBIDE-SILICON CARBIDE COMPOSITION pertains to an alumina-based matrixcontaining a dispersion of SiC whiskers and a TiC phase. The SiCwhiskers comprise 1.0 to less than 30 volume percent with the mostpreferred range being 2.5 to 20 volume percent. The TiC comprises 5 to40 volume percent, and preferably, with up to 3 volume percent of asintering aid residue.

U.S. Pat. No. 5,427,987 to Mehrotra et al. for a GROUP IVB BORIDE BASEDCUTTING TOOLS FOR MACHINING GROUP VIB BASED MATERIALS concerns zirconiumboride, hafnium boride and especially titanium boride cutting tools. Theaddition of W and Co to the boride powder improves the densification ofthe composition.

The 1969 Air Force Report by Whitney et al. mentions the use of agenerally high content of particle reinforcement in ZrN and HfN matricesfor use as cutting tools. In this 1969 Report there is no suggestionthat whiskers could reinforce these matrices.

U.S. Pat. No. 5,231,060 to Brandt teaches using whiskers of the nitride,carbides and borides of Ti, Zr, Hf, V, Nb or Ta to reinforce anoxide-based matrix such as alumina for use as a cutting tool.

U.S. Pat. No. 5,439,854 to Suzuki et al. pertains to a cutting tool thatcontains 40 weight percent or more of TiC, and 5 to 40 weight percent ofsilicon carbide whiskers (of a length equal to 20 micrometers or less).The cutting tool may also contain up to 40 weight percent alumina, aswell as sintering aids. Up to 40 weight percent of the TiC may besubstituted by Ti or a Ti-based compound such as a nitride, boride, oroxide.

Table I set forth below presents certain physical properties of someprior art commercial cutting tools.

TABLE I Selected Physical Properties of Certain Commercial Cutting ToolsVHN (GPa) [18.5 kg K_(IC)(E&C) Cutting Tool HRA load] [MPam^(1/2)]WG-300 94.6 19.4 6.1 HC6 94.6 19.4 5.1 K090 94.8 19.1 4.7

Referring to these commercial cutting tools, the WG-300 cutting tool issold by Greenleaf Corporation of Saegertown, Pennsylvania and has acomposition of about 25 volume percent SiC whiskers and the balancealumina. The HC6 cutting tool is sold by NTK Cutting Tool Division ofNGK Spark Plugs (U.S.A.), Inc. of Farmington Hills, Mich., and has acomposition of about 70 weight percent TiC and the balance alumina. TheK090 cutting tool is made by Kennametal Inc. of Latrobe, Pa. and has acomposition of about 70 volume percent alumina and 30 volume percentTiC. Each of these compositions may also contain minor amounts ofsintering aid.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved ceramic cuttingtool, and a composition thereof, that has whisker reinforcement.

It is still another object of the invention to provide an improvedceramic cutting tool, and a composition thereof, that has ceramicwhisker reinforcement wherein the ceramic matrix includes about 50volume percent of one or more of the carbides, nitrides and/orcarbonitrides of titanium, hafnium molybdenum, zirconium, tantalum,niobium, vanadium and/or tungsten.

It is another object of the invention to provide an improved ceramiccutting tool, and a composition thereof, that has ceramic whiskerreinforcement wherein the ceramic matrix includes about 50 volumepercent of one or more of the carbides, nitrides and/or carbonitrides oftitanium, hafnium, molybdenum, zirconium, tantalum, niobium, vanadiumand/or tungsten, and optionally, the substrate further includes one ormore particulates of alumina, silicon carbide or the borides oftitanium, zirconium or hafnium.

It is still another object of the invention to provide an improvedceramic cutting tool, and a composition thereof, that has ceramicwhisker reinforcement wherein the whiskers include one of alumina,silicon carbide, or the carbides, nitrides, borides or carbonitrides oftitanium, zirconium or hafnium.

It is another object of the invention to provide an improved ceramiccutting tool, and a composition thereof, that has ceramic whiskerreinforcement wherein the ceramic matrix includes about 50 volumepercent of one or more of the carbides, nitrides and/or carbonitrides oftitanium, hafnium, molybdenum, zirconium, tantalum, niobium, vanadiumand/or tungsten, and optionally, the substrate further includes one ormore particulates of alumina, silicon carbide or the borides oftitanium, zirconium or hafnium. The ceramic whiskers include one or moreof alumina, silicon carbide, silicon nitride, boron carbide, or thecarbides, nitrides, borides, or the carbonitrides of titanium, zirconiumor hafnium, or the oxides of zirconium or hafnium.

In one form thereof, the invention is a composition produced by theconsolidation of a blend of starting components. The compositioncomprises a matrix which comprises one or more of the carbides, nitridesand carbonitrides of hafnium, molybdenum, zirconium, tantalum, niobium,vanadium, titanium, tungsten and solid solutions thereof in an amountthat is greater than 50 volume percent of the matrix. The matrix furtherincludes sintering aid residue present from the use of one or moresintering aids as a starting component in an amount of less than orequal to 1 weight percent of the starting components. The matrixcomprises between 60 and 99.8 volume percent of the composition. Thecomposition further includes ceramic whiskers uniformly dispersedthroughout the matrix wherein the ceramic whiskers comprises between 0.2and 40 volume percent of the composition.

In another form thereof, the invention is a ceramic cutting tool thatcomprises a rake face and a flank face. There is a cutting edge at thejuncture of the rake face and the flank face. The tool includes aceramic composition that has a matrix comprising between about 45 volumepercent and less than 50 volume percent of titanium molybdenum carbide,and less than about 55 volume percent alumina. The matrix comprisesbetween about 60 volume percent and about 90 volume percent of theceramic composition. The composition further includes ceramic whiskersuniformly dispersed throughout the matrix wherein the ceramic whiskerscomprise about 2 volume percent to about 35 volume percent of theceramic composition.

BRIEF DESCRIPTION OF THE FIGURES

The following is a brief description of the figures that comprise a partof this patent application:

FIG. 1 is an isometric view of a cutting insert that comprises aspecific embodiment of the cutting tool of the present invention; and

FIG. 2 is a scanning electron microscopy (SEM) secondary electron imagephotomicrograph (5000X magnification) of a hot-pressed composite inaccordance with the present invention corresponding to Example 2 hereinshowing a polished plane perpendicular to the hot pressing axis;

FIG. 3 is a scanning electron microscopy (SEM) secondary electron imagephotomicrograph (2000X magnification) of a hot-pressed composite inaccordance with the present invention corresponding to Example 4 hereinshowing a polished plane perpendicular to the hot pressing axis;

FIG. 4 is a scanning electron microscopy (SEM) secondary electron imagephotomicrograph (2000X magnification) of a hot-pressed composite inaccordance with the present invention corresponding to Example 6 hereinshowing a polished plane perpendicular to the hot pressing axis;

FIG. 5 is a graph of depth of cut notch wear as a function of cuttingtime for embodiments of the present invention as well as a prior artcomposition;

FIG. 6 is a graph of flank wear as a function of cutting time forembodiments of the present invention as well as a prior art composition;and

FIG. 7 is a graph of nose wear as a function of cutting time forembodiments of the present invention as well as a prior art composition.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The invention pertains to ceramic compositions, and especially, suchceramic compositions that include ceramic whisker reinforcement.Generally speaking the ceramic cutting tool comprises a ceramic matrixand ceramic whiskers which reinforce the matrix. The combination of thematrix and the whiskers comprises a substrate. The substrate may becoated with a hard material. Examples of such hard materials includealumina, titanium carbide, titanium nitride, titanium carbonitride,titanium aluminum nitride, cubic boron nitride and diamond and theircombinations. The coating may be applied by chemical vapor deposition(CVD) [see U.S. Pat. No. 4,801,510 to Mehrotra et al. for ALUMINA COATEDSILICON CARBIDE WHISKER-ALUMINA COMPOSITION] or physical vapordeposition (PVD) [see U.S. Pat. No. 5,264,297 to Jindal et al. forPHYSICAL VAPOR DEPOSITION OF TITANIUM NITRIDE ON A NONCONDUCTIVESUBSTRATE] or a scheme where some layers are applied by PVD and somelayers are applied by CVD (see U.S. Pat. No. 5,232,318 to Santhanam etal. for COATED CUTTING TOOLS). The substrates that have a high titaniumcarbide or titanium carbonitride content, i.e., at least 25 to 30 volumepercent titanium carbide or titanium carbonitride, are electricallyconductive to such an extent that they are particularly suitable for PVDcoating and EDM machining.

The specific matrix of the present invention comprises a carbide,carbonitride and/or nitride of one or more of titanium, hafnium,molybdenum, zirconium, tantalum, niobium, vanadium and/or tungsten sothat this component is about 50 volume percent or more of the matrix.

The reason that the preferable content for the carbide, nitride,carbonitride component is over 50 volume percent of the matrix is thatthis provides for higher hardness and a higher fracture toughness. Inthis regard, when the carbide, nitride, carbonitride component is over50 volume percent of the matrix, the fracture toughness is greater thanor equal to 6.3 MPam^(½) K_(IC), and more preferably greater than orequal to 6.6 MPam^(½) K_(IC), and the hardness is greater than or equalto 94.7 Rockwell A. The combination of the high hardness and the highfracture toughness makes these combinations suitable for use as cuttingtools, bearings, seal rings, wear plates and nozzles.

In addition, the matrix may include particulates of silicon carbide,titanium boride, zirconium boride, chromium boride, hafnium boride,alumina, zirconium oxide, and hafnium oxide along with sintering aidresidues. The preferred content of the sintering aids is less than orequal to 1 weight percent, and the more preferable sintering aid contentis less than or equal to 0.5 weight percent. The preferred sinteringaids include yttria, magnesia and zirconia either alone or incombination.

The matrix comprises between 60 and 99.8 volume percent of the completeceramic cutting tool composition.

In regard to the ceramic whiskers, these whiskers are selected from anyof the following materials: silicon carbide, titanium carbide, titaniumcarbonitride, titanium nitride, titanium boride, zirconium carbide,zirconium carbonitride, zirconium nitride, zirconium boride, hafniumcarbide, hafnium nitride, hafnium carbonitride, hafnium boride, alumina,silicon nitride and boron carbide. The ceramic whiskers comprise between0.2 and 40 volume percent of the complete ceramic cutting toolcomposition.

To maximize fracture toughness in the present invention, it is preferredthat a Group IVB (titanium, hafnium or zirconium) nitride orcarbonitride-based matrix, more preferably a titanium nitride ortitanium carbonitride-based matrix, be reinforced with one or morewhiskers of the group consisting of Al₂O₃, Si₃N₄, TiB₂, SiC, TiC, andB₄C. The TiC, TiB₂, SiC or B₄C whiskers should provide the best fracturetoughness in a titanium nitride or titanium carbonitride-based matrix.

Referring to FIG. 1 and the geometry of the specific embodiment, thereis illustrated a cutting tool generally designated as 10. Cutting tool10 has a rake face 12 and a flank face 14. The rake face and the flankface intersect to form a cutting edge 16. The specific configuration isa SNGN-453T style of cutting insert with a T land according to theAmerican National Standard for Cutting Tools-IndexableInserts-Identification System, ANSI B212.4-1986 (cutting edgepreparation: 0.002-0.004 inch ×20° chamfer). Other styles of cuttinginserts and edge preparations are acceptable and are contemplated to bewithin the scope of this invention.

As demonstrated from the examples below, ceramic cutting tools withinthe above definition have excellent density, hardness and fracturetoughness. These properties provide for excellent cutting tools,especially in the high speed machining of steels, cast irons, andnickel-base super alloys.

In machining applications where abrasive wear resistance is more of aconcern than chemical wear resistance, a titanium carbide-based matrixis preferable. If, however, chemical wear resistance is more importantthan abrasive wear resistance, then a hafnium carbide-based or titaniumcarbonitride-based matrix is preferable. Chemical wear resistance mayalso be improved by applying a hard coating to the insert such as, forexample, titanium nitride, titanium carbonitride, titanium aluminumnitride, titanium carbide, and alumina.

For machining of nickel base super alloys, or for any workpiece in whicha combination of high hardness and high chemical inertness is desired,it is preferred that a titanium carbonitride (TiC_(x) N_(y)) basedmatrix be used in which x is greater that 0 but less than 0.95 andy+x=1. More preferably, y is greater than or equal to 0.5. For x=0, thatis titanium nitride, hardness may be reduced and there may be a reactionbetween the titanium nitride and the SiC whiskers during the hightemperature fabrication of these materials. Therefore, y should be lessthan 0.95. Optionally, titanium carbonitride may be replaced by hafniumcarbonitride or zirconium carbonitride.

The following examples, as described in Tables II through IV below, areexemplary of the invention and were made according to the followingmethod. For all of the examples, the silicon carbide whiskers wereultrasonically dispersed in isopropanol for one hour.

For Examples Nos. 1 through 7, 9 and 10, the silicon carbide whiskerswere made by Tokai Carbon Co. of Tokyo, Japan under the designationGrade No. 1. The Tokai whiskers had an average length of 20 to 50micrometers and an average diameter of 0.3 to 1 micrometers. Thecrystalline structure of these Tokai SiC whiskers was mostly betasilicon carbide.

For Examples Nos. 11 and 12, the silicon carbide whiskers were obtainedfrom Advanced Composite Materials Corporation of Greer, South Carolinaunder the grade designation SC-9. The SC-9 whiskers had an averagelength of 10 to 80 micrometers and an average diameter of 0.6micrometers. The crystalline structure of these SC-9 SiC whiskers wasalpha silicon carbide.

In regard to the method of preparation for Examples Nos. 1 through 7 and9 through 12, the balance of the components were blended in a mill withisopropanol for one hour. The ultrasonicated silicon carbide whiskerswere then blended with the blend of the balance of the components in amill for 20 minutes. This blend was then discharged through a 200 meshscreen, dried in a rotary evaporator, and then passed through a 100 meshscreen. The dried blend was uniaxially hot pressed in a temperaturerange of 1750° C. to 1850° C. at 4500 psi for 60 minutes under an argonatmosphere to essentially full density. The resulting product was groundinto a SNGN-453T style of cutting insert having a T land, (cutting edgepreparation of 0.002 to 0.004 inches and 20 degrees chamfer) asdescribed above.

Tables II through IV below includes in parenthesis the identification ofthe supplier if there was more than one supplier of the component. TheY₂O₃ for all of the examples was supplied by Hermann C. Strack BerlinGmbH & Co, KG, P O Box 1229, D-7887 Lauterburg, Baden, Germany.

In Tables II through IV the silicon carbide whiskers supplied by Tokaicarry the designation “(T)”. The silicon carbide whiskers supplied byAdvanced Composite Materials Corporation carry the designation “(A)”.

For some of the examples, the Al₂O₃ was supplied by NanophaseTechnologies Corporation of Darien, Ill. under the designation NanotekAl₂O₃ Gamma/Delta. In Tables II through IV, the designation “(N)” showsthat the Al₂O₃ powder was obtained from Nanophase. The Nanotek Al₂O₃powder had a BET specific surface area of 56.2 square meters/gram. TheAl₂O₃ was greater than 99.9% pure. The phases present were delta andgamma. For the example (Example No. 2) that used the Nanotek Al₂O₃powder, an addition of 0.05 volume percent MgO was added to the blend.The Nanotek Al₂O₃ powder was substantially equiaxed.

The balance of the examples used Al₂O₃ from several lots of Al₂O₃ powderthat were supplied by Ceralox (a division of Vista Chemical Company)under the designation HPA-0.5. In Tables II through IV the designation“(C)” shows that the Al₂O₃ was from Ceralox. The Ceralox powder had aBET specific surface area of 10.0 to 11.5 square meters/gram. Theas-received Ceralox Al₂O₃ contained an addition of 0.05 volume percentMgO. The Ceralox Al₂O₃ powder was substantially equiaxed.

The TiC supplied by Biesterfeld U.S. Inc., Advanced Materials Departmentof New York, N.Y. carried the designation Furukawa TiC, and had a BETspecific surface area of 8.52 square meters/gram. In Table II thedesignation “(F)” shows that the TiC was Furukawa TiC. The Furukawa TiCpowder was substantially equiaxed.

The TiC particles supplied by the Macro Division of Kennametal Inc.under the designation Grade A had a BET specific surface area of 5.9square meters/gram. In Table II the designation “(M)” shows that the TiCcame from the Macro Division of Kennametal. The Macro Division TiCpowder was substantially equiaxed.

The Ti_(0.8)Mo_(0.2)C solid solution powder supplied by the MacroDivision of Kennametal Inc. of Port Coquitlam, British Columbia, Canadahad a BET specific surface area of 4.6 square meters/gram. TheTi_(0.8)Mo_(0.2)C solid solution powder was substantially equiaxed.

The titanium carbonitride powder supplied by the Macro Division ofKennametal Inc. had a BET specific surface area of 5.2 squaremeters/gram. This component has a formula of TiC_(0.7)N_(0.3). The MacroDivision titanium carbonitride powder was substantially equiaxed.

Tables II through IV below set forth the compositions (and supplierswhere indicated) and the hot pressing temperature. The compositions areset forth in volume percent of the entire composition. For thosecomponents that are a part of the matrix, the volume percentage of thematrix for that component is set forth in brackets. For all of Examples1 through 7 and 9 through 12 the alumina component contained about 0.05volume percent magnesia.

In addition, Tables II through IV below set forth the results of teststo ascertain the following properties of the examples: the density(grams/cc), the Rockwell A hardness, the Vickers hardness, and thefracture toughness (MPam^(½)) as measured by Evans & Charles (Evans &Charles, “Fracture Toughness Determination by Indentation”, J. AmericanCeramic Society, Vol. 59, Nos. 7-8, pages 371-372 using a 18.5 kg load).

TABLE II TiC—Al₂O₃—SiC Whisker Compositions and Physical Properties ofExamples Nos. 1-3, 9 and 10 Ex./Comp & Physical Example PropertiesExample 1 Example 2 Example 3 Example 9 10 TiC 39.75(F) 39.75(F)39.75(M) 40(M) 50(M) [53] [53] [53] [62] [59] TiC_(.7)N_(.3) — — — — —Ti_(.8)Mo_(.2)C — — — — — Al₂O₃ 35(C) 35(N) 35(C) 24.75(C) 34.75(C)[46.7] [46.7] [46.7] [37.7] [40.7] Y₂O₃ 0.25 [.3] 0.25 [.3] 0.25 [.3]0.25 [.3] 0.25 [.3] SiC_(W) 25(T) 25(T) 25(T) 35(T) 15(T) Temp (° C.)1750 1750 1775 1800 1800 Density 4.147 4.147 4.137 4.069 4.318 (g/cc)HRA 95.0 95.1 94.9 94.9 94.7 VHN (Gpa) 21.0 20.8 19.7 21.1 20 [18.5 kgload] K_(IC) (E&C) 6.3 6.3 6.6 7.2 6.7 MPam^(1/2)

TABLE III TiC_(.7)N_(.3)-Alumina-SiC Whisker Compositions and PhysicalProperties of Examples Nos. 4, 7, 11 and 12 Ex./Comp. & PhysicalProperties Example 4 Example 7 Example 11 Example 12 TiC — — — —TiC_(.7)N_(.3) 39.03 39.75 39.75 39.75 [52.5] [53] [53] [53]Ti_(.8)Mo_(.2)C — — — — Al₂O₃ 35.43(C) 35(C) 35(C) 35(C) [47.4] [46.7][46.7] [46.7] Y₂O₃ 0.25 [.3] 0.25 [.3] 0.25 [.3] 0.25 [.3] SiC_(W)25.29(T) 25(T) 25(A) 25(A) Temp (° C.) 1800 1800 1800 1850 Density 4.2144.228 4.223 4.241 (g/cc) HRA 95.0 95.0 94.8 94.9 VHN (Gpa) 20.7 21.119.8 20.1 [18.5 kg load] K_(IC) (E&C) 6.3 6.6 7.5 7.5 MPam^(1/2)

TABLE IV Ti_(.8)Mo_(.2)C-Alumina-SiC Whisker Composites Compositions andPhysical Properties of Examples Nos. 5 and 6 Ex./ Comp. & PhysicalProperties Example 5 Example 6 TiC — — TiC_(.7)N_(.3) — —Ti_(.8)Mo_(.2)C 34.7 [47.6] 39.75 [53] Al₂O₃ 38(C) [52] 35(C) [46.7]Y₂O₃ 0.27 [.4] 0.25 [.3] SiC_(W) 27.03(T) 25(T) Temp. (° C.) 1800 1800Density (g/cc) 4.371 4.473 HRA 95.2 95.0 VHN (Gpa) 20.7 21.3 [18.5 kgload] K_(IC) (E&C) 6.3 6.5 MPam^(1/2)

A review of the physical properties of the examples reveals that thesecompositions present physical properties that should make excellentcutting tools.

For example, referring to the physical properties of the composites ofTable II, Examples Nos. 1 through 3, 9 and 10 present compositions ofTiC, alumina and SiC whiskers. The densities for these compositionsranged from 4.069 g/cc to 4.318 g/cc. The Rockwell A hardness (HRA)ranged from 94.7 to 95.1 and the Vickers Hardress ranged from 19.7 to21.1. The fracture toughness K_(IC) (E&C) ranged from 6.3 to 7.2MPam^(½).

A comparison of Example 10 with Example 9 shows that an increase in theTiC content (from 40 vol. % to 50 vol. %) and the alumina content (from24.75 vol. % to 34.75 vol. %) coupled with a decrease in the SiC whiskercontent (from 35 vol. % to 15 vol. %) results in an increase in thedensity of the sintered composite from 4.069 g/cc to 4.318 g/cc.

Referring to all of the examples of Table II, there does not appear tobe any discernible trend in the hardness parameters (Rockwell A andVickers).

A comparison between Examples Nos. 1 and 2 shows that the coarseness ofthe alumina powder does not significantly impact the physicalproperties.

Still referring to the composites in Table II, a comparison betweenExample 9 and Examples Nos. 1 through 3 reveals that the fracturetoughness (K_(IC)) appears to significantly increase when the aluminacontent decreases and the silicon carbide whisker content increases.More specifically, with the TiC content remaining the same, a decreasein alumina from about 35 vol. % to about 25 vol. % coupled with anincrease in the silicon carbide whisker content from about 25 vol. % toabout 35 vol. % results in an increase in the fracture toughness(K_(IC)) from between 6.3 and 6.6 to 7.2 MPam^(½).

A comparison of Example 9 with Example 10 reveals that fracturetoughness [K_(IC)] increases from 6.7 to 7.2 MPam^(½) when the TiC andalumina contents decrease and the SiC whisker content increases.

Referring to the physical properties of the TiC_(0.7)N_(0.3)-alumina-SiCwhisker composites in Table III, it becomes apparent that the use of theSC-9 silicon carbide whiskers from Advanced Composite MaterialsCorporation provides for an increase in the fracture toughness of thisTiCN-alumina-SiC whisker composite from between 6.3 and 6.6 to 7.5MPam^(½). Although the compositions are somewhat similar, the increasein fracture toughness appears to be due to the nature of the SC-9whiskers as compared to the Tokai silicon carbide whiskers.

Referring to the examples (Examples Nos. 5 and 6) of Table IV thatpresent the physical properties of the Ti_(0.8)Mo_(0.2)C-alumina-SiCwhisker composites, a comparison between Examples Nos. 5 and 6 showsthat a decrease of 5 volume percent in the Ti_(0.8)Mo_(0.2)C coupledwith a 3 volume percent increase in the alumina and a 2 volume percentincrease in the SiC whiskers does not make a significant impact on theproperties of the Ti_(0.8)Mo_(0.2)C—Al₂O₃—SiC whisker composite.

Overall, it can be seen that the above composites in accordance with thepresent invention possess a combination of hardness and fracturetoughness which are unequaled by the prior art cutting tool compositionsshown in Table I.

Photomicrographs which are representative of examples of thecompositions in accordance with the present invention are shown in FIGS.2, 3, and 4. In FIG. 2, which corresponds to Example 2, the lightestphase is alumina, the gray phase is titanium carbide, the elongated (ordarkest) phase are silicon carbide whiskers. In FIG. 3, whichcorresponds to Example 4, the lightest phase is also alumina and thedarkest phase is also silicon carbide whiskers, however, the gray phaseis titanium carbonitride. In FIG. 4, which corresponds to Example 6, thelightest and darkest phases are respectively alumina and silicon carbidewhiskers, however, the gray phase is titanium molybdenum carbide.

In accordance with the present invention, the compositions of Examples1, 3, 4, 6, and 7 shown in Tables II were ground into SNGN-453Tindexable cutting inserts and used to machine Inconel 718 (hardness 38Rockwell C) in a turning test under the conditions of 800 surfacefeet/minute speed, 0.006 inch per revolution, feed rate, and 0.050 inchdepth of cut, flood coolant, and a 45 degree lead angle. The end of lifecriteria used was: flank wear (FW)=0.030 inch; maximum flank wear(MW)=0.040 inch; nose wear (NW)=0.040 inch; depth of cut notch(DN)=0.080 inch; and crater wear (CR)=0.004 inch. Included in the testswere samples of WG-300 (Example No. 8) in the same insert geometry forcomparison purposes. The results of these tests are shown in Table Vbelow and in FIGS. 5, 6, and 7. Each example is identified in FIGS. 5, 6and 7 by its identical reference numeral. These results indicate thatthe tools having a matrix based on titanium carbonitride or titaniummolybdenum carbide had the best cutting edge life time under the aboveconditions. The most rapid wear mechanism and the wear mechanism whichlead to failure was depth of cut notching on all the materials shown inTable V.

TABLE V Tool Life & Failure Mode for Examples Nos. 1, 3, 4, 6, 7 andWG-300 Tool Life Relative % Rep. 1 Rep. 2 Average Tool Life Example(Minutes) (Minutes) (Minutes) vs. WG-300 1 5.8 DN 1.5 DN 3.7  78% 3 4.3DN 1.3 DN 2.8  60% 4 9.7 DN 8.8 DN 9.3 197% 6 7.3 DN 6.4 DN 6.9 146% 74.7 DN 6.9 DN 5.8 123% 8 4.3 DN 5.1 DN 4.7 100%

However, the flank wear resistance of the present invention was lessthan that of the prior art grade tested. It is believed that flank wearresistance may be improved by increasing the nitrogen content of thetitanium carbonitride forming the matrix or increasing the molybdenumcontent of the titanium molybdenum carbide used in the matrix. Flankwear resistance of the present invention may also be improved byapplying a hard coating to the cutting insert composed of compositionsin accordance with the present invention. Preferred hard coatingsinclude titanium nitride, titanium carbonitride, titanium aluminumnitride, and alumina coatings applied by PVD and/or CVD techniques.

The flank wear resistance of the prior art grade tested (Example No.8/WG-300) appeared to be better than Examples Nos. 1, 3, 4, 6 and 7.This may be due to the greater alumina content in the prior art grade.More specifically, the prior art grade (Example No. 8/WG-300) has analumina content of about 75 volume percent as compared with about 35 to40 volume percent for Examples Nos. 1, 3, 4, 6 and 7. The flank wearresistance of the present invention may be improved by the use ofgreater amounts of alumina or by decreasing the amount of siliconcarbide whiskers present and increasing one or more of the matrixphases, e.g., titanium carbonitride or alumina.

All applications, patents and other documents referred to herein arehereby incorporated by reference herein.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as illustrative only, with the true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. A composition produced by the consolidation of ablend of starting components, the composition comprising: a matrixcomprising one or more of the carbides, nitrides and carbonitrides ofhafnium, molybdenum, tungsten, zirconium, tantalum, niobium, vanadium,titanium, and solid solutions thereof in an amount that is greater than50 volume percent of the matrix, the matrix further includes sinteringaid residue present from the use of one or more sintering aids as astarting component in an amount less than 0.5 weight percent of thestarting components wherein the sintering aid comprises one or more ofyttria, magnesia and zirconia, the matrix comprising between 60 and 99.8volume percent of the composition; and ceramic whiskers uniformlydispersed throughout the matrix, the ceramic whiskers comprising between0.2 and 40 volume percent of the composition.
 2. The composition ofclaim 1 wherein the ceramic whiskers comprise silicon carbide whiskers,and the silicon carbide whiskers having an average length between about20 micrometers and about 50 micrometers, an average diameter of betweenabout 0.3 micrometers and about 1 micrometer, and the crystallinestructure of the silicon carbide whiskers is predominantly beta siliconcarbide.
 3. The composition of claim 2 wherein the fracture toughness ofthe ceramic cutting tool is equal to or greater than about 6.3MPam^(½)K_(IC) and a hardness of greater than or equal to 94.7 RockwellA.
 4. The composition of claim 1 wherein the ceramic whiskers comprisesilicon carbide whiskers, and the silicon carbide whiskers having anaverage length between about 10 micrometers and about 80 micrometers, anaverage diameter of about 0.6 micrometers, and the crystalline structureof the silicon carbide whiskers is predominantly alpha silicon carbide.5. The composition of claim 4 wherein the fracture toughness of theceramic cutting tool is equal to or greater than about 7.5MPam^(½)K_(IC) and a hardness of greater than or equal to 94.7 RockwellA.
 6. A ceramic cutting tool comprising: a rake face; and a flank face,a cutting edge at the juncture of the rake face and the flank face; aceramic composition having a matrix comprising at least 50 volumepercent of one or more of the carbides, nitrides and carbonitrides ofhafnium, molybdenum, zirconium, tantalum, niobium, vanadium, tungsten,titanium, and solid solutions thereof, the matrix further includessintering aid residue present from the use of one or more sintering aidsas a starting component in an amount less than 0.5 weight percent of thestarting components wherein the sintering aid comprises one or more ofyttria, magnesia and zirconia, wherein the matrix comprises between 60and 99.8 volume percent of the ceramic composition; and ceramic whiskersuniformly dispersed throughout the matrix wherein the ceramic whiskerscomprise between 0.2 and 40 volume percent of the ceramic composition.7. The ceramic cutting tool of claim 6 wherein the ceramic cutting toolfurther includes a coating, and the coating comprises a layer selectedfrom the group consisting of alumina, titanium carbide, titaniumnitride, titanium carbonitride, and titanium aluminum nitride.
 8. Theceramic cutting tool of claim 7 wherein the layer is applied by chemicalvapor deposition.
 9. The ceramic cutting tool of claim 7 wherein thelayer is applied by physical vapor deposition.
 10. The ceramic cuttingtool of claim 7 wherein the ceramic whiskers are silicon carbidewhiskers.
 11. The ceramic cutting tool of claim 10 wherein the siliconcarbide whiskers having an average length between about 20 micrometersand about 50 micrometers, an average diameter of between about 0.3micrometers and about 1 micrometer, and the crystalline structure of thesilicon carbide whiskers is predominantly beta silicon carbide.
 12. Theceramic cutting tool of claim 11 wherein the fracture toughness of thecoated ceramic cutting tool is equal to or greater than 6.6MPam^(½)K_(IC) and a hardness of greater than or equal to 94.7 RockwellA.
 13. The ceramic cutting tool of claim 10 wherein the silicon carbidewhiskers having an average length between about 10 micrometers and about80 micrometers, an average diameter of about 0.6 micrometers, and thecrystalline structure of the silicon carbide whiskers is predominantlyalpha silicon carbide.
 14. The ceramic cutting tool of claim 13 whereinthe fracture toughness of the coated ceramic cutting tool is equal to orgreater than 7.5 MPam^(½)K_(IC) and a hardness of greater than or equalto 94.7 Rockwell A.
 15. A method of cutting metal wherein a ceramiccutting tool is brought into contact with a metal workpiece and theceramic cutting tool and metal workpiece move relative to each otherwhereby metal is removed by the ceramic cutting tool from the metalworkpiece using a ceramic cutting tool comprising: a rake face and aflank face wherein the rake face and the flank face intersect to form acutting edge; the composition of the ceramic cutting tool comprising amatrix including: titanium carbonitride in an amount of about 50 volumepercent or more of the matrix; alumina in an amount that is greater thanabout 40 volume percent of the matrix; and sintering aid residue presentfrom the use of one or more sintering aids as a starting component in anamount less than 0.5 weight percent of the starting components whereinthe sintering aid comprises one or more of yttria, magnesia andzirconia; the matrix comprising between 60 and 99.8 volume percent ofthe composition of the ceramic cutting tool; the composition of theceramic cutting tool further comprising ceramic whiskers uniformlydispersed throughout the matrix, the ceramic whiskers comprising between0.2 and 40 volume percent of the composition; the titanium carbonitridehaving the formula Ti(C_(x)N_(y)) wherein y is less than 0.9 and greaterthan or equal to 0.5, and x+y=1; and the ceramic cutting tool having afracture toughness of greater than or equal to about 6.3 MPam^(½)K_(IC)and a hardness of greater than or equal to about 94.7 Rockwell A. 16.The method of claim 15 wherein the ceramic whiskers comprise siliconcarbide whiskers, and the silicon carbide whiskers having an averagelength between about 20 micrometers and about 50 micrometers, an averagediameter of between about 0.3 micrometers and about 1 micrometer, andthe crystalline structure of the silicon carbide whiskers ispredominantly beta silicon carbide.
 17. The method of claim 15 whereinthe ceramic whiskers comprise silicon carbide whiskers, and the siliconcarbide whiskers having an average length between about 10 micrometersand about 80 micrometers, an average diameter of about 0.6 micrometers,and the crystalline structure of the silicon carbide whiskers ispredominantly alpha silicon carbide.
 18. The method of claim 17 whereinthe fracture toughness of the composition is equal to or greater than7.5 MPam^(½).
 19. The method of claim 15 wherein the ceramic cuttingtool includes a coating, and the coating comprises a layer selected fromthe group consisting of alumina, titanium carbide, titanium nitride,titanium carbonitride, and titanium aluminum nitride.
 20. The method ofclaim 19 wherein the coating layer is applied by chemical vapordeposition.
 21. The method of claim 19 wherein the coating layer isapplied by physical vapor deposition.
 22. The ceramic cutting tool ofclaim 6 wherein the ceramic cutting tool further comprising a coatingscheme comprising one layer of titanium carbonitride and another layerof alumina.
 23. The ceramic cutting tool of claim 22 wherein the layerof titanium carbonitride and the layer of alumina is each applied bychemical vapor deposition.
 24. The ceramic cutting tool of claim 6further comprising a coating scheme comprising a first layer of titaniumcarbonitride applied to at least a portion of one or both of the rakeface and the flank face, and the coating scheme further including asecond layer of alumina.
 25. The ceramic cutting tool of claim 24wherein the second layer of alumina being applied to the surface of thefirst layer of titanium carbonitride.
 26. The method of claim 15 whereinthe ceramic cutting tool includes a coating, and the coating comprisinga first layer of titanium carbonitride and a second layer of alumina.27. The method of claim 26 wherein the first layer of titaniumcarbonitride being applied to at least a portion of one or both of therake face and the flank face.
 28. The method of claim 27 wherein thesecond layer of alumina being applied to the first layer of titaniumcarbonitride.
 29. The method of claim 26 wherein the first layer oftitanium carbonitride and the second layer of alumina is each applied bychemical vapor deposition.
 30. A coated ceramic cutting tool comprising:a substrate presenting a rake face and a flank face, a cutting edge atthe juncture of the rake face and the flank face; the substrate having acomposition comprising a matrix comprising at least 50 volume percent ofone or more of the carbides, nitrides and carbonitrides of hafnium,molybdenum, zirconium, tantalum, niobium, vanadium, tungsten, titaniumand solid solutions thereof, the matrix further comprising the sinteraid residue present from the use of one more sintering aids as astarting component in an amount less than 1 weight percent of thestarting components wherein the sintering aid comprises one or more ofyttria, magnesia, and zirconia, wherein the matrix comprises between 60and 99.8 volume percent of the substrate composition; ceramic whiskersuniformly dispersed throughout the matrix wherein the ceramic whiskerscomprises between 0.2 and 40 volume percent of the substratecomposition; and a coating on at least a portion of the substrate. 31.The coated ceramic cutting tool of claim 30 the coating comprising layerselected from the group consisting of alumina, titanium carbide,titanium nitride, titanium carbonitride, and titanium aluminum nitride.32. The coated ceramic cutting tool of claim 30 wherein the matrixcomprising titanium carbonitride in an amount of about 50 volume percentor more of the matrix, alumina in an amount that is greater than about40 volume percent of the matrix; and the ceramic wiskers comprisingsilicon carbide whiskers.
 33. The coated ceramic cutting tool of claim32 wherein the matrix comprising between about 70 volume percent andabout 90 volume percent of the substrate composition, and the siliconcarbide whiskers comprising between about 10 volume percent and about 30volume percent of the substrate composition.